Methods of fabricating transistors having excellent performance characteristics have been researched. In order to implement high-performance transistors, many methods of increasing the mobility of electrons or holes have been developed. Methods of increasing the mobility of electrons or holes in MOSFETs include methods of changing the energy band structure of a channel region by applying physical stress to the channel region. For example, in the case of an NMOS transistor, the performance thereof may be improved when tensile stress is applied to a channel, and in the case of a PMOS transistor, the performance thereof may be improved when compressive stress is applied to a channel. Moreover, because the performance of the NMOS transistor and the PMOS transistor can be simultaneously improved by forming a tensile stress layer in the NMOS transistor and a compressive stress layer in the PMOS transistor, it may be preferable to employ dual stress layers. In the case where dual stress layers are employed, a region may exist in which a tensile stress layer and a compressive stress layer partially overlap each other in a boundary region between an NMOS transistor and a PMOS transistor. The region in which the stress layers overlap each other may be thicker than those regions having a single stress layer. Accordingly, if a contact hole passing through a single stress layer and a contact hole passing through the overlap region are simultaneously formed through an etching process, a lower structure may not be exposed and part of a stress layer may remain in the overlap region even though the contact hole in the single stress layer exposes the lower structure. Accordingly, contact may not be achieved in the overlap region. Furthermore, when etching is performed for a sufficient period or using high-concentration etching gas so as to completely pass through the overlap region, a contact hole is formed in the single stress layer. When this occurs, the lower structure may be excessively exposed to the etching gas, and the lower structure may be damaged.